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REDIA, 108, 2025: 83-89 http://dx.doi.org/10.19263/REDIA-108.25.09
Received 10 January 2025 Accepted 20 February 2025
INTRODUCTION
The tribe Xyleborini LeConte (Coleoptera, Curculio-
nidae, Scolytinae) is a taxon globally widespread across
various ecosystems, with particularly high biodiversity
in tropical and subtropical areas such as Southeast Asia
( and , 2013; et al., 2015). The
investigation of this group is fundamental as many of its
species are harmful pests in either forest or agriculture
environments. The strong ability of these beetles to in-
vade and establish in new geographical areas together,
with their well-documented polyphagy and elevated like-
lihood of encountering suitable host species (e.g. Xylo-
sandrus crassiusculus, X. compactus, and X. germanus,
in Italy) make them one of the foremost phytosanitary
which these pests may attack host plants and potentially
introduce pathogenic organisms into plant tissues is also
of paramount concern for the preservation of orchards
-
-
se poorly known Xyleborine species globally inhabiting
tropical forests may harbor potentially pathogenic and
yet uncharacterized fungi.
In the mid of May 2024, the National Reference In-
stitute for Plant Protection was contacted by an agrono-
mist technician requesting to examine plant specimens
located in a private facility in the Municipality of Monte-
chiarugolo (Parma) and suspected of xyleborine ambro-
sia beetle infestations.
On 27 May 2024, the facility containing plants was
thoroughly inspected: specimens of Xyleborine ambrosia
beetles as well as other bark beetles were collected from
a Ficus macrophylla tree grown for ornamental purpo-
ses. The tree had been originally shipped to Italy from
a specialized plant nursery located in Alicante (Spain).
This plant was a mature specimen characterized by a
central stem from which thin but long branches extended
outwards. On the main stem, minute perforations asso-
observed while screening the colonized plant for insect
activity. During the inspection of the facility, additional
insect specimens were detected within the building, spe-
to the plant.
MATERIALS AND METHODS
All inspections in the inner tissues of the tree were
carried out using suitable cutting tools (e.g. hatchets, kni-
ves, gouges, chisels). Once insect activity was detected, a
total of 8 wood samplings colonized by bark beetles were
collected at the base of the stem and the main branches,
placed into plastic bags, properly coded, and transported
to the CREA-DC (Research Centre for Plant Protection
in
planta and laboratory investigations, a special focus was
placed on detecting penetration and/or emergence holes
and possible insect gallery systems indicating potential
ambrosia beetle infestations. In the laboratory, all live
organisms detected in the wood samplings and, more ge-
a - SALVATORE VITALEb - DOMENICO RIZZOc - LAURA LUONGOb -
a - IVANA GARAGUSOb a - b -
EMILIO RESTAd a
aCREA - DC – Italian National Reference Institute for Plant Protection / Research Centre for Plant Protection
and Certication, via Lanciola 12/A, 50125, Florence, Italy.
bCREA - DC – Italian National Reference Institute for Plant Protection / Research Centre for Plant Protection
and Certication, via C.G. Bertero 22, 00156 Rome, Italy
cLaboratory of Phytopathological Diagnostics and Molecular Biology, Plant Protection Service of Tuscany,
Pistoia, Italy
dDr. Agronomo libero professionista, via Carrara - Capannori (LU), Italy
fabrizio.pennacchio@crea.gov.it
Euwallacea similis (
Xyleborini)
Euwallacea similis
on an ‘ornamental’ Ficus macrophylla tree, based on a series of specimens collected in Montechiarugolo (Parma,
Alien insects, Ambrosia beetles, Ficus macrophylla.
84 ET AL. REDIA, Vol. 108 2025
nerally, all material including insect-related wood parts
such as frass and debris, were collected and placed into
plastic containers. All these specimens were subsequent-
ly analyzed in the CREA-DC (INRPP) facilities/labora-
tories.
-
on the description of and (2013) and
the keys of et al-
microscope equipped with a cold light source. The main
diagnostic characters of beetles were then photographed
by Scanning Electron Microscopy (Model) using spe-
-
ed, mounted on stubs, and coated with gold-palladium
DNA extraction from 4 adults of Euwallacea si-
milis was performed according to protocols establi-
shed in previous works ( et al., 2022). Each
sampling was extracted in triplicate and the obtained
using a Spectrophotometer QiaExpert (Qiagen, Hilden,
was assessed by qPCR with a probe targeting a highly
conserved region of the eukaryote 18S rDNA ( et
al. 2009).
Hercules, CA, USA) following the procedures described
by and , (2014), except for COI whe-
re the standard EPPO procedures were applied: EPPO
PM7/129 (2) (tab. 1).
All the produced amplicons were sequenced at the
-
and the inferred sequences compared with sequences
-
fore being aligned by the software Geneious Prime®
2025.0.2.
RESULTS
On the inspected Ficus macrophylla tree, insect acti-
vity was detected either externally on the stem or inter-
nally within maternal galleries excavated at the subcorti-
cal level or in the wood tissues.
It was noted that, prior to penetrating the wood tissue,
females had constructed a brief longitudinal subcortical
tunnel (measuring approximately 5.8 cm in length): this
structure was morphologically irregular and it was cha-
racterized, occasionally, by lateral transverse extensions,
-
thout any observed formation of vestibules.
Moreover, adult excavation activities had led to a
-
gated forming small cones concealing the minute circular
entrance holes. In some cases, this extruded frass could
also form typical tiny and compact cylindrical structu-
res. The intensity and magnitude of the infestation were
so pronounced that the entire stem appeared colonized
(i.e. from the sticking out roots, at the collar level, to the
top of the stem encompassing the main branches). The
severity of the attack was immediately evident because
of the considerable layers of extruded frass accumulated
at the base of the plant. Similarly, this material could be
(Tav. I).
-
All the evaluated Xyleborine beetles were morpholo-
Euwallacea similis
a non-EU Scolytinae species listed in the Commission
Implementing Regulation 2019/2072 as Scolytinae spp.
species in Europe
through molecular analyses of Xyleborine specimens.
In particular, sequences of CAD, 28S, and ArgK of the
Xileborine beetles under study were almost completely
identical to sequences of Euwallacea similis
Tab. 1
Gene Primers Sequences First cited
COI LCO 1490 5’-GGTCAACAAATCATAAAGATATTGG-3’ PM7/129 (EPPO)
HCO 2198 5’-TAAACTTCAGGGTGACCAAAAAATCA-3’ PM7/129 (EPPO)
28S 5’-AGACAGAGTTCAAGAGTACGTG-3’ and 1997
5’-TTGGTCCGTGTTTCAAGACGGG-3’ and 1997
CAD
et al., 2010
apCADrev1mod et al
apCADfor4 et al
apCADrev1mod et al., 2010
ArgK et al., 2010
5’-GTATGYTCMCCRCGRGTACCACG-3’ et al., 2010
... 85
-
neious Prime® 2025.0.2 by aligning our sequences with
sequences in the database belonging to the same gene.
In the light of morphological and molecular resul-
-
duction Protection of the Emilia-Romagna Region was
E. similis.
DISCUSSION
In their native habitats, scolytids, with the exception
of a limited number of species, are generally harmless or
only moderately harmful to host plants; however, their
impact can dramatically change once introduced into
new environments. There is evidence, that trade of host
plants may increase the risk of accidental introductions
of alien species, playing, thus, a crucial role in their es-
tablishment beyond the native geographic distribution.
A pertinent example of this phenomenon is Polygra-
phus proximus, which, once accidentally introduced into
Central Siberia, was strongly attracted to the local conif-
erous forests such as Abies sibirica Ledeb., ( et
al., 2013, , 2025). Xyleborines beetles belonging
to the Euwallacea fornicatus species complex and Xy-
leborus glabratus
North American plants and Israeli Avocado crops (-
et al., 2020; et al., 2012; et al.,
2017). Moreover, E. fornicatus was also recently record-
ed in Spain (et al., 2025) on Acer negun-
do and Parkinsonia sp. Nonetheless, it is worth noting
colonized areas are frequently the result of intricate in-
teractions occurring among the host plants, the insects,
and the associated fungi, as evidenced in the aforemen-
tioned examples ( et al., 2017; et al.,
2018; et al., 2023). Therefore, the introduction
of organisms such as opportunistic fungi, potentially ex-
hibiting pathogenic characteristics, may often contribute
Tav. 1 - Extensive colonization of Ficus macrophylla by Euwallacea similis. Note the abundant presence of compact frass (top left) and
a section of the trunk with emergence holes (bottom right).
ET AL. REDIA, Vol. 108 2025
to the decline of the host plants leading to their ultimate
death. Since xylophagous Xyleborine beetles, such as E.
similis, excavate maternal tunnels extensively within the
woody structures of host plants and are known to carry
pathogenic fungi, they are regarded as a taxonomic group
posing considerable threats to plants in the agricultural,
forestry, and ornamental sectors ( et al., 2023).
E. similis a is a well-known strongly polyphagous
species with 145 known host plants (
et al., 2023). It is a non-Euro-
pean scolytid (Regulation EU 2072/2019 Annex Part II
-
racterized by low or uncertain impacts on plant health
it is able to infest a wide range of plants either within
newly established ecosystems or even in its native range
-
cies such as Acacia, which is extensively cultivated in
Vietnam ( et al.
(subsquared pronotum) and it is distinguishable by the
declivital interstriae 1 broadened laterally, bearing a large
median tubercle as well as many small granules (rarely
median tubercles absent) (, 2007;
et al., 2020). Equally characteristic are its small
body size and the elongate form as well as its red brown
color. The distribution of this species ranges from the In-
dian subcontinent, through southeast Asia and Indonesia,
as tropical Africa and Indian Ocean islands. It was also
-
qing, Guangdong, Hainan, Hong Kong, Yunnan), India
(Andaman Is, Assam, Jharkhand, Karnataka, Madhya
Pradesh, Nicobar Is, Sikkim, Tamil Nadu, Uttarakhand,
Taiwan, Thailand, Vietnam and it was accidentally in-
troduced into the USA ( et al., 2014;
et al et al., 2018) as well as Central and
South America (, 2007).
Its gallery system is formed by typical branched tun-
nels extending in either one horizontal plane or into three
dimensions penetrating deeply into the wood. In small
diameter stems, the galleries may be longitudinal. No
brood chambers have been observed, so far, regardless
of gallery type.
As regards molecular analysis, it should be evidenced
that DNA barcoding has emerged as a well-established
the examination of standardized sequence data: this is
particularly true for the cytochrome oxidase subunit I
(COI) gene, which is prevalent among various organisms
between distinct species. This method is useful in taxo-
nomy since species may exhibit morphological similarity
insect taxa, including those belonging to the Xyleborini
tribe and particularly to the genus Euwallacea (
and , 2014). In many cases, the application of
species within various insect taxa, particularly within the
Xyleborini tribe. Such a technique appears crucial when
conventional morphological approaches fail to deline-
ate species boundaries due to pronounced similarities
among closely related taxa ( and , 2014).
Nonetheless, the incorporation of multiple DNA loci, in-
cluding COI, 28S, CAD, and ArgK, has been evidenced
to improve the resolution of phylogenetic relationships
among Scolytinae species, thereby promoting a more
evolutionary patterns ( and , 2014). Spe-
Euwallacea similis
... 87
for their phylogenetic relevance and their capability to
clarify taxonomic uncertainties within the Scolytinae cla-
de ( and , 2014).
In our study, results observed from COI analysis
could be explained based on empirical evidence as well
as studies, conducted over the years, concerning species
within the genus Euwallacea ( et al., 2024).
et al.,
-
tors such as polyphagy, inbreeding, and insect capacity
to acclimatize to new environments. All of these factors
might determine variations in mitochondrial genetic di-
versity, a characteristic often observed in species with
inbreeding systems, while the nuclear genetic variability
might remain relatively minimal or absent ( et
al., 2019).
gene, are in line with the investigation conducted by -
et al
clarify the use of the DNA sequences corresponding to
of Scolytinae species within the Xyleborini tribe. A par-
-
nomenon that has also been documented in prior research
involving a selection of species from the Xyleborini tribe
( et al., 2010; et al., 2011).
Nonetheless, as this is a clade of scolytinae beetles
solely based on morphological or molecular parameters,
an integrated approach combining classical morphologi-
cal systematics with molecular biology has been advoca-
ted by several authors including et al. (2020).
In the very next future, in a context of increasing trade
of commodities and, thus, potential biological invasions,
crucial importance for policymakers taking decisions on
phytosanitary issues either on a local or global scale.
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Gene Identity percentage Best matching sequence
COI
CAD 99.12 ± 0.04
28S HM099754.1
Arginine Kinase (ArgK) 99.20 ± 0.09
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